Oxidation of hydrocarbons in the presence of liquid catalytic films



Patented Jan. 3, 1950 OXIDATION OF HYDROCARBONS IN. THE

PRESENCE OF LIQUID CATALYTIC FILMS Aristid V. Grosse, Haverford, and John C. Snyder,

Darling, Pa., assignors to Houdry Process Corporation, Wilmington, Del., a corporation of Delaware No Drawing. Application December 19,1947,

' Serial No. 792,848

11 Claims. (Cl. 260-451) This invention relates to oxidative reactions and particularly to the oxidation of hydrocarbons to form normally liquid oxygenated products, such as alcohols, esters, acids, ketones, aldehydes of the same or difierent number of carbon atoms than the parent hydrocarbon.

We have unexpectedly discovered, in accordance with our invention, that we can oxidize volatile hydrocarbons to oxygenated organic comcatalytic liquid being minor in respect to the' volume of the reaction zone.

We believe, although we do not wish to be bound in the practice of our invention by any theory thereof, that the superior results that we obtain in oxidations effected according to our invention are due to the use of a catalytic liquid film under conditions, as set forth herein, such that the catalytic film initiates a chain reaction which when propagates in the-vapor phase with the formation of oxygenated products. We select the reaction conditions so that the reaction does not proceed with explosive violence with consequent formation of carbon oxides as the main products. We have found that the presence of inert gaseous diluents (such as nitrogen when air is used as the source of oxygen) and low densities or abnormally high densities of reactants slow down the rate of reaction many fold whereas the use of relatively high temperatures or insuflicient cooling of the gaseous mixture causes the oxidation to proceed with undesirably rapid rates or even explosive violence with the consequent destruction of the desired products. We have further found that there is a minimum average distance between a hydrocarbon molecule in the vapor state and the catalytic liquid film below which the oxidation proceeds only slowly and that there is a critical range of density for any particular hydrocarbon in which superior results are obtained at a particular temperature.

It should be noted that an oxidation effected in accordance with our invention involves the following characteristics: (1) that it proceeds by a chain reaction; (2) that the chain reaction potentially may proceed atan undesirably high rate to give undesirable products; (3) that the reaction is capable of being catalyzed by catalysts which can be maintained as or within liquid films; (4) that it is possible to maintain the reacting materials substantially completely in the vapor phase under conditions which give practical reaction rates. Reactions of'the oxidative type (which, may include chlorination, nitration, and similar treatments of organic compounds such as hydrocarbons) frequently have these characteristics and our concept may be applied thereto. The manner in which our concept may be applied canbe understood by the description herein of an exemplary operation applied to the oxidation of hydrocarbons by molecular oxygen.

As pointed out above, we obtain superior results when the reacting materials are substantially completely in the vapor phase and when we use a catalytic liquid in the form of a thin film, which is preferably flowing. Such a film and the manner of its use are essential features of our invention. We have found that, under the same conditions, virtually no reaction occurs in the absence of such a film and little, if any, reaction occurs with a film when the film contains no catalyst or the catalytic effect is neutralized by the presence of an oxidation inhibitor. The catalytic liquid forming the film may itself be a catalyst or it may comprise a carrier liquid containing a catalyst either in suspension or solution. A carrier liquid is preferably inert to oxidation or is similar or identical to one or more of the oxidation resistant products of the oxidation. Thus, for example, acetic, propionic, or butyric acids, carbon tetrachloride, benzene, phenylacetic acid, acetic anhydride, water and the like may be used as a carrier liquid for organic or inorganic salts or oxides of cerium, cobalt, copper, manganese, silver or uranium; or other liquids or catalysts such .as those disclosed in Patent No. 2,265,948 issued to D. J. Loder on December 9, 1941, may be used. Furthermore, the liquid may contain, as disclosed in this patent, various initiators. Whether or not the catalytic film is a catalyst alone, such as cobalt stearate, or is a carrier liquid containing a catalyst in solution,

such as glacial acetic containing cobalt acetate,

or in suspension, such as colloidal osmium in amount of liquid present in the reaction zone at any given time should be minor in respect to the volume of the reactant vapors present in the reaction zone.

The function of the catalytic liquid is to present a catalyzing surface to the gaseous reactantsfand the thickness of the film formed by the liquid may therefore vary depending on its nature and manner of use, but, since superior results in regard to the rate and/or selectivity of the reaction are dependent on conducting the reaction substantially completely in the gaseous phase, it is preferred, as noted above, that the amount of the catalytic liquid present in the reaction zone shouldbe minor-in respect to the volume of gaseous reactants present in the reaction zone in order that the maximum amount of space be available for the chain reaction in gaseous phase. Under these conditions, we obtain a high reaction rate and gain the added advantage that the catalytic liquid dissolves a minimum amount for gaseous reactants (solution of considerable quantities of the gaseous reactants in the catalytic liquid tends to give undesirably low reaction rates). We have found that, when we control the depth of the liquid film so that the volume of the catalytic liquid is less than 10 volume per cent of the volume of the gaseous react ants, the effect is advantageous, and that particularly advantageous results are obtained when the volume of liquid is less than volume per cent of the volume of the gaseous reactants, such as apreferred range of from about 0.01 to about 2 volume per cent.

In addition to the relative amount of the liquid, the relation of the extent of liquid surface to the volume of the gas phase is an important factor. When the liquid film flows over a surface which is also a heat exchange surface as,

for example, the interior of a metallic vessel the exterior temperature of which is controlled as by heating or cooling, we have found that the distance between opposing film surfaces, which is a measure of the average distance of a molecule of reactant to the surface covered by the catalytic liquid film, should preferably be greaterthan about 0.3 to 0.4 millimeter. This distance should not be too great and is preferably less than 20 centimeters in the absence of some means of cooling the gas phase other than by heat exchange at thewalls of the reaction zone. The distance between the opposing liquid films may be conveniently expressed as the ratio of the surface of the catalytic film to the volume of the gaseous reactants (i e. the volume of the vapor phase). (The ratio referred to has the dimension of length and may be expressed as reciprocal centimeters or reciprocal feet). We have found, as a result of our investigations, that this ratio should be between about 0.2 to about 100 reciprocal centimeters and preferably between about 0.5 to about 20 reciprocal centimeters.

The effect of this ratio is one of the reasons for our belief that the reaction, when effected in accordance with our invention, is propagated as a chain reaction in the gaseous phase and is different from the usual liquid phase reaction in the catalytic liquid or a simple homogeneous gas phase reaction. If the reaction occurred principally at the interface between the catalytic film and the'gaseous phase, the absolute value of the surface of the catalytic film should be more important than the ratio of the surface of the film to the volume of the gaseous phase. In order to ascertain the effect of surface, we filled a reaction zone with packing in the form of glass wool on which was maintained a film of catalytic liquid consisting of cobalt acetate in acetic acid, and contacted this film with a mixture of butane and molecular oxygen under pressure. A similar run was made under identical conditions, except that the packing was absent, and the catalytic liquid was maintained as a flowing film on the walls of the vessel. The rate of oxygen absorption (in gram atoms. per hour per liter of reaction volume) was about 1.7 times more rapid for the oxidation conducted in the unpacked zone (which had a ratio of surface area of the film to volume of the gaseous phase of about 1.15 reciprocal centimeters) than for the oxidation conducted in the packed zone (where the same ratio was about 116). Thus, in spite of a hundredfold increase in surface area, the reaction was slower. It should be noted, however, that the reaction space ,can be packed to advantage with loose packing, as, for example, Berl saddles or Raschig rings.

The film may be formed from the catalytic liquid by various methods, such as by flowing the liquid down the walls of a cylindrical vessel or over packing selected to give the proper surfacevolume relations described herein, or by spraying a mist or droplets of the catalytic liquid into the reaction zone or by combinations of these and similar methods.

As stated above, we have found that it is important that the volume of the catalytic liquid occupy a minor portion of total reaction zone (or, in other words, that the ratio of the volume of the catalytic liquid to the volume of the gas phase be small). In our investigations, we found that, under otherwise identical conditions, an oxidation of butane in which the catalytic liquid occupies about 1 volume per cent of the reaction zone has a rate of oxygen absorption and a production of liquid oxygenated products more than 3 times greater than an oxidation conducted under identical conditions except that the catalytic liquid occupies about 25 volume per cent or more of the reaction zone. We'also found that when the volume of the gaseous phase was maintained approximately constant but the volume of the catalytic liquid was increased eightfold (but was still minor in respect to the volume of the gaseous phase), the rate of oxygen absorption was approximately the same. Moreover, in all of the above oxidations performed in accordance with our invention, less than 5 per cent of the hydrocarbon material reacted was converted to carbon oxides (i. e. greater than conversion to useful products). As can be understood from the above data, one of the factors in obtaining superior results in oxidations performed according to our invention is the maintenance of only a minor amount of the catalytic liquid in the reaction zone, relative to total volume of the reaction zone, an effective maximum being about 10 volume per cent, particularly advantageous results being obtained when amount of the catalytic liquid is less than 5 volume per cent, such as 0.02 to 2 volume per cen As stated above, it isadvantageous to effect the oxidation under conditions that maintain the maximum amount of reactants in the gaseous phase. This effect is aided, as stated above, by maintaining a relatively minor amount of the catalytic liquid in the reaction zone. We also prefer to maintain temperature and pressure conditions such that the hydrocarbon is 7 substantially completely in the vapor phase.

Oxidative reactions may be eflected, according to our invention. over a considerable range of pressures from substantially above atmospheric pressure, such as above about atmospheres to relatively high superatmospheric pressures, such as about 300 atmospheres, the reaction \rate being considerably reduced outside these values where the same amount of oxygen is used. A particularly effective range is between about to about 100 atmospheres, and preferably between about to about "15 atmospheres. Similarly a wide range of temperatures may be used, the reaction being generally conducted above a temperature at which oxidation is slow, such as about 100 C. and below a temperature of about 300 C. We prefer to use conditions of temperature and pressure that are correlated so that the hydrocarbon material in the'reaction zone does not condense to form a liquid phase; such a condition is obtained by maintaining the hydrocarbon material above its dew point (the dew point of a condensible vapor being defined as that temperature and partial pressure at which reduction of temperature or increase of pressure causes the appearance of a liquid phase in a previously completely gaseous phase). Our invention, therefore, includes in its scope the oxidation of hydrocarbons whose boiling point at pressure substantially above atmospheric pressure, such as 5 atmospheres, is below the practical upper limit of temperature above which excessive formation of carbon oxides results. When the oxidation is effected under conditions such that 300 C. or above is the practical upper limit, suitable hydrocarbons will include volatile low molecular weight hydrocarbons that are substantially completely in the vapor phase at pressures of about 10 atmospheres or more at 300 C.

In accordance with a preferred embodiment of our invention; we oxidize at least one volatile low molecular weight hydrocarbon of the type described below at pressure substantially above the dew point of the hydrocarbon or hydrocarbons being oxidized by maintaining the reaction zone at a temperature above the dew point of said hydrocarbon or hydrocarbons and below about 210 C., such temperatures preferably being above about 125 C. In connection with this embodiment, we prefer to oxidize hydrocarbon material consisting essentially of at least one of the relatively volatile aliphatic hydrocarbons having from two to five carbon atoms inclusive, such as the paraffin hydrocarbons from ethane to pentane, inclusive, or the mono-olefins from ethylene or pentene. In general, we prefer to select, from among the broad ranges of conditions, those conditions which are suited to the reactivity of the particular hydrocarbon being oxidized and thus employ less severe conditions as the molecular weight, extent of molecular branching or extent of unsaturation increases.

We have found, as stated above, that the presence of inert diluents, such as nitrogen, decreases the rate of oxidation. As a means of increasing the rate of reaction we may use concentrated molecular oxygen, which may be obtained, for example, by the fractionation of liquid air. Such concentrated oxygen preferably contains less than volume per cent of inert diluents, superior results being obtained when the oxygen contains less than 5 volume per cent, such as 2 per cent or less, of such diluents.

The concentration or partial pressure-of hydrocarbon material in e reaction zone is, according to our invention, maintained considerably in excess of the concentration of the 111016011? lar oxygen inthe reaction zone, an effective ratio 5. of t e concentrations of hydrocarbon to oxygen being more than four to one, such as from about ten to one to fifty to one. Low relative concentrations of oxygen with high yields of liquid products may also =-be obtained by adding the oxygen in successive increments, the addition of these incrementsf being spaced apart by time intervals such that the majority ofethe previous increment of oxygen has reacted before-a-follow ing i1icr err ent .is;v introduced into the reaction zone. I .In order to -illustrate'the present invention but not to, be construed as. alimitation thereof, the

following exampl ia e given:

2o Emmpte I A stainless steel bomb, adapted to be rocked through an angle of 60at a'rate of'one cycle per second, wascharged with 37.60 grams (649'millimoles) of n-buta'ne' imore than"'99% pure), 1.7 milliliters (hereafter abbreviated as'ml.) of glacial acetic acid and"1.0 ml. of'g lacial acetic acid containing 2 weight per cent of cobalt acetate. The 1.7 m1. of acetic acid charged was calculated to be the amount which would vaporize at 160 C. in the volume available (the volume of the bomb being about 210 ml), thus insuring the maintainance of a liquid film. The 1.0 ml. of cobalt acetate in acetic acid was calinterior surface of the bomb and provide a flowing thin film when the bomb was rocked as described above. The -bomb and contents were heated to 160 C. and thereafter maintained at this temperature, the pressure in the bomb after heating being 5'75 pounds per square inch gauge (hereafter abbreviated as p. s. i. g.)

Concentrated molecular oxygen (over 99% pure) was added until the pressure was 625 p. s. i. g. After 5 minutes, 8.1 millimoles of oxygen were added after which the pressure was 655 p. s. i. g., whereupon a rapid reaction occurred as evidenced by a surge in pressure of about p. s. i. g. followed by a rapid drop ,in pressure to about 6 1 5 p. s. i. g. The procedure outlined above was periodically repeated for 2 hours, with essentially the same results (i. e. a surge in pressure following the addition of oxygen followed by a rapid decrease in pressure and finally a leveling out at approximately a constant pressure), there being a total of 22 injections of oxygen varying from about 5 to about 25 nullimoles of oxygen per injection amounting to a total of 263 millimoles.

The bomb was cooled and the contents removed and analyzed, the oxygenated derivatives being identified and determined by standard methods. A total of 31.06 grams of unreacted butane was recovered indicating that 17.4 per.

culated to be the amount necessary to wet the 7 acted butane or 0.5 mole of butyl acetate equals 75 per cent of 1 mole of butane reacted).

Per Cent Compound Carbon dioxide and carbon monoxide Acetaldehyde Ethylaoetate Ethanol Sec-Butyl acetate. Acetic acid bi- H co -menu In the above table, the amount of acetic acid initially present is not considered a product.

Example I1 Percent of Compound reacted Carbon dioxide and carbon monoxide Acetone Methanol tert.-Butsnol Acetic acid Unidentified rem-i853 Example III Using the same apparatus and procedure and the same amount of acetic acid and cobalt acetate as in Example I, 37.71 grams of Z-butene (of more than 99 per cent purity) were oxidized at 160 C., using 169 millimoles of oxygen in one hour. Analysis of the contents of the bomb showed that 19.2 per cent of the butene-2 had reacted as had 92.4 per cent of the oxygen. The liquid products, on a butene-free basis, amounted to 14.00 grams,

was

Isobutane exclusive of the acetic acid originally charged.

The products, on the basis stated above, were as follows:

I Per cent Carbon dioxide and carbon monoxide 3.4 2,3-but-ylene glycol 39 Acetic acid 12 Acetaldehyde 12 Sec-butanol Ethanol 8 Higher glycols and others (calculated as having the composition of butylene glycol) 15 The 2,3-butylene glycol was found partially condensed as glycol acetates, acetaldehyde was found partially as acetals with ethanol and some of the acetic acid was condensed with ethanol as ethylacetate.

Example IV butene-free basis, amounted to 9.18 grams, exclusive of the aceticacid originally charged.

The data indicated that only 2.9 per cent of the hydrocarbon reacted had been converted to car-'- bon dioxide and carbon monoxide. The liquid products were found to consist mainly of esters of 1,2-butylene glycol, together with some formic and propionic acid and some higher boiling compounds of butylene glycol. 7

Example V Using the same apparatus procedure and the same amount of acetic acid and cobalt acetate as in Example I, 36.58 grams of isobutene (of 99 per cent purity) were oxidized at 0., using 198 millimoles of oxygen in two hours. Analysis of the contents of the bomb indicated that 28.2 per cent of the hydrocarbon had reacted.

The data showed that 3.7 per cent of the hydrocarbon reacted had been converted to carbon dioxide and carbon monoxide. The liquid prodnets, on an isobutene-free basis, amounted to 13.16 grams, exclusive of the acetic acid originally charged, and were composed principally oi glycols, glycol esters, formic acid and acetone.

Example VI were the same, but a variable vapor density (or' pressure) of n-butane at the start of the run before the injection of any oxygen was employed in the different runs. The following results were obtained:

Vapor density of n-butane (in grams per ml.) .0.002 0.09 0.13 0.18 0.33 Oxygen absorption in miiiitoms per hour pcrliter oi reaction space 0 300 450 1300 500 the vapor density was 0.13 gram per ml., and

about four times as much as when the vapor density was 0.33 gram per ml., further indicating the superiority of conducting the oxidation in the range of density (or pressure) stated.

These data confirm the view that the reaction may be slowed down by too great a density of the reactants, probably due to an extinction of the chain reaction at an early stage due to overcrowding of the molecules in the gaseous state.

Example VII Using the same apparatus and procedure and the same amount of acetic acid and cobalt acetate as in Example I, 10.94 grams of isopentane were oxidized at 160 C. using 13 injections of oxygen over a period of six hours, the total amount of oxygen used being 186 millimoles. It was calculated that, at the stated conditions, the amount of isopentane used was insuillcient to give a liquid phase. Analysis of the contents of the bomb indi- Example VIII Using the same apparatus and procedure and the same amount of acetic acid and cobalt acetate as in Example I, 28.3 grams of propylene (of more than 99 per cent purity) were oxidized at 180 C.,

using 23 injections of oxygen over a period of 88 minutes, the total amount of oxygen used being 306 millimoles. Analysis of the contents of the bomb indicated that 1'70 millimoles or 27 per cent of the propylene had reacted.

Analysis of the liquid products from this and another run made under almost identical condi-' tions showed that a small amount of acetaldehyde had been formed, and that the liquid products boiling above 120 C. consisted principally of mixed formic and acetic esters of 1,2-propylene glycol. The material boiling above the esters mentioned consisted mainly of ester and ether condensation products of 1,2-propylene glycol. The fraction boiling below 120 C. contained free acetic and formicacids, as well as considerable amounts of isopropyl esters and acetals of formic and acetic acids with formaldehyde and acetaldehyde.

Obviously many modifications and variations of the invention as hereinbefore set forth may be made without departing from the spirit and scope thereof and therefore only such limitations should be imposed as are indicated in the appended claims.

We claim as our invention:

1. In the oxidation of a volatile low molecular weight aliphatic hydrocarbon to form oxygenated 40 organic compounds, the improvement which comprises reacting said hydrocarbon with molecular oxygen under conditions adapted to maintain said hydrocarbon substantially completely in the vapor phase at superatmospheric pressures of at least 5 atmospheres and in the presence of a catalytic liquid in the form of a thin film, the volume of said liquid being minor in respect to the volume occupied by the gaseous reactants.

2. The improvement of claim 1 in which the 60 3. In the'oxidation of avolatile low molecular weight aliphatic hydrocarbon to form oxygenated organic compounds, the improvement which comprises reacting said hydrocarbon with concentrated molecular oxygen under conditions adapted to maintain said hydrocarbon substantially completely in the vapor phase at superatmospheric pressures of at least 5 atmospheres and in the presence of a catalytic liquid in the form of a thin film, the volume of said liquid being between about 0.01 to about 2 per cent of the volume occupied by the gaseous reactants.

4. The improvement of claim 3 in which the ratio of the surface of said film to the volume of 2,009,663

the vapor phase is between about 0.2 to about reciprocal centimeters.

5. The improvement of claim 3 in which the ratio of the'surface or said film to the volume of the vapor phase is between about 0.5 to about 20 reciprocal centimeters.

6. In the oxidation of a volatile low molecular weight aliphatic hydrocarbon to form oxygenated organic compounds, the improvement which comprises reacting said hydrocarbon with molecular oxygen in the presence of a catalytic liquid in the form of a thin fllm and at a temperature in the range of about 100 C. to about 300 C. and at a superatmospheric pressure of at least 5 atmospheres, said temperature and pressure being above the dew point oi said hydrocarbon so as to maintain said hydrocarbon substantially comletely invapor phase, the volume of said catalytic liquid being minor in respectto the volume occupied by the gaseous reactants.

7. In the oxidation of a volatile low molecular weight aliphatic hydrocarbon to form oxygenated organic compounds, the improvement which com.-

prises reacting said hydrocarbon with molecular oxygen in the presence of a catalytic liquid in the form oi a thin film and at a temperature in the range of about C. to about 210 C., and a superatmospheric pressure of at least 5 atmospheres, said temperature and pressure being above the dew point of said hydrocarbon so as to maintain said hydrocarbon substantially completely in vapor phase, the volume of said catalytic liquid being minor in respect to the volume occupied by the gaseous reactants.

8. The improvement of claim 7 in which the molecular oxygen contains less than 5 volume per cent of inert diluents.

9. The improvement of claim '7 in which the ratio of said hydrocarbon and molecular oxygen is less than 10 to 1.

10. The improvement oi claim '7 in which the oxygen is periodically added in small increments.

11. In the oxidation of n-butane to form oxygenated organic compounds, the improvement which comprises reacting n-butane with concentrated molecular oxygen at a temperature or about C. and at a partial pressure of nbutane in the reaction zone between 550 to 700 pounds per square inch and in the presence of a catalytic liquid in the form of a thin film, the volume of said liquid being between about 0.01 and about 2 per cent oi the volume occupied by the gaseous reactants.

ARISTDV. GROSSE. JOHN c. SNYDER.

REFERENCES crr'nn The following references are of record in the file of this patent:

UNITED STATES PATENTS Name Date James Dec. 26, 1933 James July 30, 1935 Number Certificate of Con-cation Patent No. 2,492,985 January 3, 1950 ARISTID v. GROSSE ET AL.

It is hereby certified that errors appear in the printed specification of the above numbered patent requiring correction as follows:

f r OZIdumn 1, 31, for the word "when read than; column 3, line 20, for amount 0 re amoun o r and that the said Letters Patent should be read with these corrections therein that the same may conform to the record of the case in the Patent Ofiice.

Signed and sealed this 6th day of June, A. D. 1950.

THOMAS F. MURPHY,

Assistant aommiuioner of Patcn'ta. 

1. IN THE OXIDATION OF A VOLATILE LOW MOLECULAR WEIGHT ALIPHATIC HYDROCARBON TO FORM OXYGENATED ORGANIC COMPOUNDS, THE IMPROVEMENT WHICH COMPRISES REACTING SAID HYDROCARBON WITH MOLECULAR OXYGEN UNDER CONDITIONS ADAPTED TO MAINTAIN SAID HYDROCARBON SUBSTANTIALLY COMPLETELY IN THE VAPOR PHASE AT SUPERATMOSPHERIC PRESSURES OF AT LEAST 5 ATMOSPHERES AND IN THE PRESENCE OF A CATALYTIC LIQUID IN THE FORM OF A THIN FILM, THE VOLUME OF SAID LIQUID BEING MINOR IN RESPECT TO THE VOLUME OCCUPIED BY THE GASEOUS REACTANTS. 